The present invention relates to a gas turbine installation, especially for the drive of motor vehicles, with a combustion chamber for producing the operating medium of the output turbine, whereby the combustion chamber is constructed as two-stage combustion chamber with catalytic combustion in the first stage constructed as head combustion chamber, as well as to a method for operating such a gas turbine installation.
In the prior art design of combustion chambers for gas turbines which are to be used in motor vehicles, especially in passenger motor vehicles, one has placed heretofore a value only on achieving a high combustion degree and a uniform temperature distribution.
By reason of more strict legal regulations in the exhaust gas sector of internal combustion engines, an increased attention must now be paid also in connection with the construction of gas turbines and in particular of the combustion chambers thereof to the prescribed harmful materials emission limits. The influencing magnitudes to be taken into consideration in the design which are determinative for the harmful material generation, result from the analysis of the reaction-kinetic processes in the combustion chamber. The most important influencing magnitudes are thereby the primary zone temperature and the equivalence ratio, the degree of the pre-mixing and of the combustion homogeneity in the primary zone, the dwell of the combustion products in the primary zone, the "freezing-in" of the reaction products in wall proximity of the combustion chamber and the intermediate zone temperature and dwell.
The difficulty of the design of combustion chambers low in emission of harmful materials consists in the contradictory effect of the influencing magnitudes on the individual harmful material components. Thus, for example, low primary zone temperatures lead to a low NO-emission, however, at the same time, to a high CO-concentration by reason of the reduced oxidation rate.
In order to solve these problems, it is known from the EP-A 0 144 094 to provide a catalytically assisted combustion in that a catalyst has been provided in the combustion chamber. By reason of the catalytically assisted combustion, the fuel oxidation can be displaced beyond the flame-out limit into very lean fuel-air ratios and low reaction temperatures. Thus, a possibility exists to reduce at the same time the NO-and CO-emission without loss in the power output yield or an increase in the fuel consumption. Liquid or gaseous hydrocarbons, carbon suspensions and hydrogen may be used as fuels in the combustion chamber.
It is the object of the present invention to provide for a gas turbine installation of the aforementioned type a space-saving construction.
The underlying problems are solved according to the present invention in that the combustion chamber is constructed as annular combustion chamber with a catalyst constructed as ring. The advantage of this solution resides in that compact dimensions of the entire installation are achieved because all feed lines for the second stage of the combustion chamber can be laid out into the annular space. The combustion air for the second stage thereby exerts a cooling action.
The flow constriction between the first and second stage in the direction toward the second stage offers the advantage that flashbacks or backfirings out of the second stage of the combustion chamber are avoided thereby.
A preferred feed possibility of the fuel into the first stage of the combustion chamber which assures a good and rapid mixing with the air is realizable according to the present invention in that the fuel is supplied to the first stage by way of a pre-evaporator. The pre-evaporator or pre-evaporators is or are thereby to be so designed and constructed that it or they effect a small pressure loss and assure an adequate hold-up or dwell time for the nearly complete evaporation of the fuel.
According to another feature of the present invention, the combustion chamber of the first stage is made up of a pre-mixing zone according to the diffusion burner principle and of a combustion zone with catalyst, in this sequence as viewed in the flow direction of the air. This offers the advantage that the already evaporated fuel is thereby mixed homogeneously with the air. A non-uniform mixing is prevented thereby so that no local fuel enrichments can take place which, upon reaching stoichiometric ratios, lead to the formation of flashbacks or flame backfirings into the altogether lean fuel-air mixture. The design of the mixing zone according to the principle of the diffusion burner therebeyond offers the advantage that the mixing periods are limited below the ignition delays.
If, according to another feature of the present invention, the catalyst is made up of several ring-shaped individual disk segments, then it is possible to create a catalyst constructed and to be manufactured in a simple manner which satisfies the requirements for a complete combustion while assuring at the same time a reduction of the NO- and CO-emission by means of a simple construction.
A preferred arrangement of the catalyst involves an arrangement in which at first the segments with low reaction temperature and then following the segments with high reaction temperature are provided, as viewed in the flow direction of the fuel-air mixture. By reason of the progressive temperature increase in the fuel oxidation, the first catalyst segments are so constructed that they become active at low reaction temperatures. The adjoining catalyst segments have a high oxidation effect so that the reaction temperature and therewith the air heat-up is increased.
According to still another feature of the present invention, the segments of the catalyst consist of a substrate with an intermediate adhesive layer and a catalyst layer applied thereon. Catalyst segments which are so constructed, can be manufactured economically. They are characterized by a support structure which consists of a substrate as well as of an intermediate adhesive layer on which the catalyst is applied by evaporation. The substrate may thereby consist of alloys of magnesium, aluminum and titanium while materials from the material group of platinum are provided as catalyst material.
The porosity of the substrate is so selected that the pressure loss remains small. For that purpose, each catalyst segment has at least fifty cells/cm.sup.2. A pressure loss in the combustion chamber is achieved thereby which is no greater than 5%.
For purposes of controlling the combustion in the second stage of the combustion chamber, it is proposed according to another feature of the present invention that the second stage of the combustion chamber be provided with controllable and adjustable air inlet openings. A controlled afterburning for the adjustment of maximum process temperatures is achieved therewith.
As the combustion chamber is constructed as annular combustion chamber, the space disposed in the longitudinal axis can be utilized for additional components. According to still another feature of the present invention, the control of the air inlet openings may thereby consist of an adjusting motor with adjusting members arranged in the longitudinal axis of the annular combustion chamber. A cooling and a heat insulation with respect to the hot walls of the combustion chamber is created thereby by the air itself. The fuel lines to the second stage of the combustion chamber may also be arranged at this location without the need to provide additional heat insulation measures, without which the fuel would evaporate in its lines so that deposits might then form which would lead to a clogging up of the lines.
By reason of the proposed combustion chamber geometry, also an adequate support for the adjusting motor and the actuating members is provided thereby so that an exact control of the air inlet openings combined with great length of life of the actuating members and of the adjusting motor is achieved therewith.
Two alternative possibilities for the control of the air inlet openings exist according to the present invention. According to one embodiment, the size of the air inlet opening is determined by a rotatable apertured ring. According to another embodiment of the present invention, the size of the inlet opening is determined by a displaceably arranged ring. A simplification--without negative influencing of the combustion in the second stage of the combustion chamber--of the control of the air inlet opening is possible according to the present invention in that the air inlet openings are arranged along the inner and outer circumference of the second stage of the combustion chamber and only the inner inlet openings are provided with a ring (apertured ring).
In order to achieve a good atomization, it is additionally proposed according to the present invention that at least one air-assisted atomization nozzle be provided for supplying the fuel in the second stage. The preferred location of the ignition devices according to the present invention is thereby the arrangement of a spark plug in direct proximity of the atomization nozzle.
A preferred method of operating the gas turbine installation with the combustion chamber constructed in accordance with the present invention resides in initiating the combustion in the second stage for starting the combustion machine. The control of the air supply in the second stage of the combustion chamber is thereby carried out as a function of the air requirement in the catalyst. Furthermore, during the acceleration and at full load, the power output of the second stage of the combustion chamber is increased. Thus, by reason of the construction of the two-stage combustion chamber, the combustion for the starting can be initiated in the combustion chamber itself and the catalyst can be heated up from behind, so to speak of. This takes place very rapidly so that already a short period of time after the start the fuel, oxidation in the first stage of the combustion chamber can be initiated.
By controlling the air supply in the second stage of the combustion chamber in dependence on the air requirements in the catalyst, it is achieved that the temperature increase in the combustion chamber can be controlled in order to achieve optimum combustion efficiency.
In order to achieve acceleration values of the gas turbine similar to the reciprocating piston engine as well as to cover power output peaks, the second stage is also suitable because the power output of the second stage of the combustion chamber can be increased for that purpose according to the present invention.